Sport often reveals true feelings about national loyalties. When the Scots watch an international game, their allegiance is usually to "anyone but England".

But when Rangers play Celtic, which side raises a Scottish nationalist flag? Neither. Rangers considers itself "British" and flies a Union Jack while Celtic is characterised as Irish, and flies the Tricolour.

The sovereignty of a nation is complicated, as Alex Salmond and his ScotNats will surely find out. And a largely unconsidered angle in the looming referendum on whether the United Kingdom will break up if Scotland becomes independent is the impact on Northern Ireland.

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